Variable acoustical reverberation system



Patented Jan. 11, 1938 I UNITED STATES PA ENT OFFICE VARIABLE ACOUSTICAL REVEBBERATION SYSTEM 7 Annui- Pflster, Woodside, N. Y., assignor to Radio Corporation of America, a corporation of Delaware Application March 21, 1935, Serial No. 12,211

17 Claims. This invention relates to the science of acoustics and deals more specifically with the reverber ation of sounds in enclosed spaces and means for control of same in conjunction with or by means of electrical circuits.

In present-day broadcasting, which usually takes place in studios which have been acoustically treated to reduce reverberation, it is frequently desiraole to change the acoustical characteristics of the studio rapidly during the course of the program in order that these characteristics may correspond to the type of program presented and thus convey to listeners the realism necessary for complete enjoyment of the program.

In the past, such changes have been attempted by two different methods, neither of which has proved entirely satisfactory because of the practical and technical limitations.

The first method, which is simple and widely used, employs a variable sound absorbing medium in the studies, such as drapes, sliding panels of tion amplitude but not the reverberation time since that depends upon the dimensions of the reverberation chamber and its surface material.

My present invention, which is a substantial improvement over the two methods mentioned above, is accomplished by comparatively simple means and'it permits the control of the reverberation time lag, as well as the amplitude and duration. In addition, it has other superior advantages which will be more fully outlined hereinafter.

The invention will be more thoroughly understood 'by referring to the accompanying drawing, in which Fig. 1 illustrates diagrammatically one form of my present invention. Fig. 2 is a partial:

modification of Fig. 1,-in which separate acoustic delay circuits have been combined into a single delay circuit.

Referring now in detail to the schematic diagram, Fig. 1, I represents the purposely highly damped room or studio whose acoustical characteristics are to be varied. Sound is picked up by microphone 2, converted into electrical energy and-passed through amplifier 3, volume control 4 and amplifier 5. A portion of the output energy of amplifier 5 is diverted at a point li, passed 5' through an amplifier l and then through volume controls 8A, 8B, 8C, to electro-acoustical transducers 9A, 9B, 90, respectively. These feed the respective .acoustic delay circuits IIIA, I 0B, IIIC,

which are of unequal lengthand which terminate 1 respectively in the exponential acoustical couplings HA, IIB,'HC. The orifices of A, NB, NC, are part of the wall surfaces of reverberation chamber l2 where the radiated sound is picked up by microphone I3 and reconverted into 1 electrical energy which passes through amplifier l4 and'volume control l5 and is then combined at point I6 with a portion of the original energy which has passed through the isolating amplifier IS. The combinedsignal then amplifier ii to the program bus l8.

Having thus described the elementary set-up of the apparatus involved, the manner in which the invention functions will be explained; Re-

ferring again to the diagram of Fig. 1, all equip- 2 ment within the dashed lines is of standardtype and essential to broadcasting. All equipment outside of these lines is accessory, although much of it is also of standard type, and serves to carry out the intention of the invention. The electro-acoustical transducers 9A, 9B, 90, controlled respectively by volume controls 8A, 8B, 80, receive their energy from tap 6 and radiate sound energy into acoustic delay circuits IOA,

tubes of non-resonating material of unequal length, the inner surfaces of which have a smooth and hard finish to insure satisfactory and uniform 'sound transmission.

passes through 20 IOB, IOC. These, in their preferred forms, are 35 The acoustical couplings A, NB, NC, con- 40 necting the acoustical delay circuits IDA, I03, I00, with reverberation chamber I! are of exponential form with theirorifices preferably mounted flush with the wall, or walls, of the reverberation chamber in compliance with the laws of acoustics forcoupling transmission lines of unequal dimensions: By virtue of this 'arrangement, sound can travel in practically one direction only, namely, from 911,83, 90 through IOA, I 03, I00, and HA, I IE, I I0, into reverberation chamber 12. As the name implies, this chamber is highly reverberant due to reflecting wall surfaces and, consequently, sound enteringvthrough A, NB, NC, decays at a slow rate.

Microphone l3 reconverts into electrical energy form, may be air.

altering the energy level normally existing at the input of amplifier l1. 7 r

In summarizing the action it is now evident that by diverting at point 6 a portion of the sound equivalent electrical energy from -2 and reconverting the same through electro-acoustic transducers 9A, 9B, 9C, it is possible to obtain in acoustical circuits IOA, I03, 3C, a delay with respect to source 2 which will depend upon the lengths of circuits 9A, 9B, 9C, and the type of transmission medium used which, in its simplest It is also evident that, without occupying excessive space, the delay circuits 7 may be made any desired length,witl1in practical limits, and thus simulate in any desired proportion the dimensions of. a room. Similarly, combinations of various acoustical delay circuits may be arranged to simulate rooms of almost any variety.

- Furthermore, by adding reverberation in chamber l2 to signals suitably delayed in circuits IDA, IUB, lflC, signals may be picked up by microphone I3 which faithfully resemble those which would be picked up by microphone 2 in room I but possessing such additional characteristics as are produced by the interposition of one or a combination of acoustical delay circuits, as for instance QA/IIA, QB/IIB, SC/HG, and such reverberation characteristics as are obtained in chamber I2. These reverberation characteristics can be varied by means of drapes, sliding panels,

etc.

As a result, there isavailable at junction is and in program circuit I8 a signal adjustable electrically in reverberation amplitude, durationandtime lag.

A modification of the above ment is shown in Fig. 2, wherein the separate acoustic delay circuits have been combined into a single delay circuit 0 and the individual. electro-acoustic transducers IOSA, I093, I090, radiate sound into said delay circuit at points unequally distant.

Although this invention has been described setting forth certain modifications, it is to be distinctly understood that the invention is not to be limited except as to those limitations which are clearly set forth in the appended claims.

What I claim is:

1. In a system for translating sound into characteristic electrical energy and for alternat ing the characteristics of the system electroacoustically, an electrical circuit, means for deriving from a certain point in the electrical circuit a portion of said characteristic electrical energy, means for feeding said derived energy through an amplifier circuit to a plurality of electro-acoustical transducers, a plurality of tubes forming a plurality of acoustical delay circuits coupled to said transducers, each one of said tubes being of unequal lengths to give a variety of delay times unequally long'with respect to each other and to any given point of the delay circuit.

circuit arrange- -2. In a system for translating sound into an equivalent electrical energy and for alternating the characteristics of the system electro-acoustically, said system having means deriving from a certain point in the electrical circuit a portion of sound equivalent electrical energy, means for feeding said energy through an amplifier circuit to a plurality of electro-acoustical transducers, a plurality of tubes forming a plurality of acoustical delay circuits connected to said transducers, each one of the tubes being of unequal lengths to give a variety of delay times unequally long with respect to each other and. to any given point of the delay circuit and means for unifying in a single self-contained enclosure of suitable de-. sign the two distinctly separate functions of I time delay and reverberation.

3, In a system for translating sound into an equivalent electrical energy and for alternating the characteristics of the system electro-acoustically, said system having means deriving from a certain point in the electrical circuit a portion of sound equivalent electrical energy, means for feeding said energy through an emplifier circuit to a plurality of electro-acoustlcal transducers, a .plurality of tubes of resonating material forming a plurality of acoustical delay circuits connected to said transducers, each one of the tubes being of unequal lengths to give a variety of delay times unequally long with respect to each other and to anygiven point of the delay circuit and means for isolating acoustically the distinctive separate functions of time delay and reverberation by means of an exponential acoustical coupling between the respective sections of the circuit.

4. In a systemfortranslating sound into an equivalent electrical energy and for alternating the characteristics of the system electro-acoustically, said system having means deriving from a certain point in the electrical circuit a portion of sound equivalent electrical energy, means for feeding said energy through an amplifier circuit to .a plurality of electro-acoustlcal transducers and a plurality of tubes forming a plurality of acoustical delay circuits, each tube being of unequal lengths' to give a variety of delay times unequally longwith respect to each other and to any given point of the delay circuit, means for unifying in a single self-contained enclosure of suitable design the two distinctly separate functions of time delay and reverberation, an exponential acoustical coupling between the respective sections of the acoustical circuit which is provided for the functions of delays and reverberations for the purpose of rendering the system unidirectional to sound waves in a chosen direction.

5. In a system for translating sound into an equivalent electrical energy and for alternating the characteristics of the system electro-acoustically, said system having means deriving from a certain point in the electrical circuit a portion of sound equivalent electrical energy, means for feeding said energy through an amplifier circuit to a plurality of electro-acousticaltransducers and a plurality of tubes forming a plurality of acoustical delay circuits, each tube being of unequal lengths to give a variety of delay times unequally long with respect to each other and to any given point of the delay circuit, means for unifying in a single self-contained enclosure of suitable design the two distinctly separate functions of time delay and reverberation, an exponential acoustical coupling between sections of an acoustical circuit of unequal dimensions to obtain faithful sound transfer from one section to another. I

6. In a system for translating sound into an equivalent electrical energy, and for alternating the characteristics of the system electro-acoustically, said system having means deriving from a certain point in the electrical circuit a portion of sound equivalent electrical energy, means for feeding said energy through an amplifier circuit to a plurality of electro-acoustical transducers and a plurality of tubes having a hard inner surface forming a plurality of acoustical delay circuits, each being of unequal lengths to give a variety of delay times unequally long with respect to each other and to any given point of the delay circuit andan isolating amplifier between that point in the circuit where a portion of the sound equivalent electrical energy is diverted for the purpose of obtaining an acoustic delay-and that point in the circuit where the delayed energy is combined with a portion of the original energy.

7. In a system for. translating sound into an equivalent electrical energy and for alternating the characteristics of the system electro-acous ically, said system having means deriving from a. certain point in the electrical circuit a portion of sound equivalent electrical energy, means for feeding said energy through an amplifier circuit to a plurality of electro-acoustical transducers, a plurality of horns forming acoustical delay circuits connected to said transducers, each horn being of unequal lengths to give a variety of delay times unequally long with respect to each other and to any given point of the delay circuit and means for varying the reverberation time of the reverberation chamber by means of a system of drapes within said reverberation chamber.

8. In a system for translating sound into an equivalent electrical energy and for alternating the characteristics of the system electro-acoustically, said system having means deriving from a certain point in the electrical circuit a, portion of sound equivalent electrical energy, means for feeding said energy through an amplifier circuit to a plurality of electro-acoustical transducers, a plurality of horns forming acoustical delay circuits connected to said transducers, each horn being of unequal lengths to give a variety of delay times unequally long with respect to each other and to any given point of the delay circuit and means for varying the reverberation time of the reverberation chamber by means of a system of sliding panels within said reverberation chamber.

9. In a system for translating sound into an equivalent electrical energy and for alternating the characteristics of the system electro-acoustically, said system having means deriving from a certain point in the electrical circuit a portion of sound equivalent electrical energy, means for feeding said energy through an amplifier circuit to a plurality of electro-acoustical transducers feeding into a plurality of tubes forming acoustical delay circuits, each tube being of unequal lengths to give a variety of delay times unequally long with respect to each other and to any given point of the delay circuit and means'for varying the reverberation time of the reverberation chamber by the use of sound absorbent material within said reverberation chamber.

10. In a system for translating sound 'into equivalent electrical energy, means for altering the characteristics of the system electro-acoustically, said system comprising means for deriving from a certain point in the electrical circuit a portion of sound equivalent electrical energy, means for'feeding said portion of energy through an amplifier circuit to an electro-acoustical transducer and into a. plurality of tubes of unequal lengths forming an acoustical delay circuit, said acoustical delay circuit being acoustically coupled to an enclosed chamber capable of producing reverberation of sound energy and means for reconverting the reverberant sound into electrical energy and applying a certain portion thereof to the first-mentioned electrical circuit at a certain point other than the firstmentioned. I

11. In a system for translating sound into proportionately equivalent electrical energy. said system having means for altering the acoustical properties of the system electro-acoustically by deriving from a certain point in the electrical circuit a portion of sound equivalent electrical energy, means for feeding said portion, of energy through an amplifier to a plurality of electrical control means and into a plurality of electro-v acoustical transducers; a plurality of tubes of unequal lengths forming acoustical delay circuits connected to said electro-acou'stical transducers, said acoustical delay circuits being acoustically coupledto an enc osed chamber capable of producing reverberation of said sound energy, means for reconverting the reverberant sound into electrical energy and applying a certa'in portion thereof to the first-mentioned electrical circuit at a certain point other than the first-mentioned.

12. A sound translatingsystem having in combination a microphone. volume control means,

an amplifier circuit and a program output circuit, a plurality of acoustical delay circuits connected to said amplifier, said acoustical delay circuits comprising a tube having a plurality of electro-acoustical transducers located at different points along said tube. an enclosed chamber acoustically coupled to said tube. a second microphone within said chamber, a second amplifier circuit connecting said second microphone to the output program circuitsubstantially near the point where said acoustical delay circuits join sa d first mentioned amplifier.

13. A sound translating system having in combination a microphone located in a studio, volume control means. an am lifier circuit and a program output circuit. a plurality of acoustical delay circuits connected to said amplifier. said acoustical delay circuits comprising a plurality of tubes each one being of a different length. having a plurality of electro-acoustical transducers plurality of acoustical delay circuits connected to' said amplifier, and a plurality of volume control devices connecting said amplifier to said acoustical delay circuits comprising .a plurality of tubes each one being of a different length, having a plurality of electro-acoustical transducers located a second amplifier circuit connecting said second microphone to the output program circuit substantially near the point where said acoustical delay circuits join said first mentioned amplifier.

15. A sound translating system having in combination a microphone located in a highly damped room, an amplifier connected to said microphone, an amplifier circuit having a junction point and a program output circuit, a plurality of electroacoustical transducers connected to the junction point of said amplifier circuit, a plurality of tubes one end of which acoustically joins said transducers, the other end of said tubes being acoustically connected to a reverberation chamber, a circuit connecting said second microphone with the junction point of said amplifier circuit to be combined with a portion of the sound energy electrical impulses of said first mentioned microphone, the impulses of both microphones being mixed and passed to said program output circuit.

16. A sound translating system having in combination a microphone located in a highly damped room, an amplifier and a volume control device connected to said microphone, an amplifier circuit having a junction point and a program output circuit, a plurality of electro-a'coustical transducers connected to the junction point of said amplifier circuit, a plurality of tubes one end of which acoustically joins said transducers, the other end of said tubes being acoustically connected to a reverberation chamber, a second microphone located within said reverberation chamber, a circuit connecting said second microphone with the junction point oi saidamplifier circuit to be combined with a portion of the sound energy electrical'impulses of said first mentioned microphone, the impulses of both microphones being mixed and passed to said program-output circuit. 7

17. A sound translating system having in combination a microphone located in a highly damped room, an amplifier connected to said microphone, an amplifier circuit having a junction point and a program output circuit; a plurality of electroacoustical transducers connected to the junction point of said amplifier circuit, a plurality of tubes of non-resonating material one end of which acoustically joins said transducers, the other end of said tubes being acoustically connected to a reverberation chamber, a second microphone located within said reverberation chamber, a circuit connecting said second microphone with the junction point of said amplifier circuit to be comblned with a portion of the sound energy electrical impulses of said first mentioned microphone, the impulses of both microphones being mixed and passed to said program output circuit. 

